1. Field of the Invention
The present invention relates in general to semiconductor packages with solder balls and a method for producing such packages and, more particularly, to an improvement in structure of such packages as well as to an improvement in the package producing method for removing outer leads exposed to the outside of the packages and for letting the packages be easily layered vertically in order for enlarging memory capacity.
2. Description of the Prior Art
With reference to FIG. 1, there is shown a plastic BGA (ball grid arrays) package which is a representative example of typical semiconductor packages with solder balls. In the drawing, the reference numeral 1 denotes a semiconductor chip. The semiconductor chip 1 is bonded to the top surface of a PCB (printed circuit board) 2 using a die bonding epoxy 3. A solder resist 4, which is provided on the bottom surface of the PCB 2, includes a plurality of holes "s" for receiving a plurality of solder balls 5 respectively, which solder balls 5 are electrically connected to the PCB 2 and protrude out of the bottom surface of the solder resist 4, thus to electrically lead the PCB 2 to the outside of the package. The holes "s" of the solder resist 4 are spaced out at regular intervals.
A plurality of pads of the semiconductor chip 1 are electrically connected to a plurality of inner leads 8 of a lead frame by means of a plurality of metal wires 7, which metal wires 7 are bonded to the chip 1 and to the inner leads 8 of the lead frame at their opposed ends respectively. The inner leads 8 include a through hole 6 at a predetermined portion, which through hole 6 is provided with a metal pattern (not shown) therein. A predetermined volume including the semiconductor chip 1 and the metal wires 7 is hermetically packaged by a plastic resin body 9.
The above plastic BGA package is produced by the following process.
The BGA package producing process is started at a die bonding step in which the semiconductor chip 1 is bonded to the top surface of the PCB 2 using the die bonding epoxy 3. The die bonding step is followed by a wire bonding step for electrically connecting the pads of the semiconductor chip 1 to the inner leads 8 of the lead frame by means of the metal wires 7. After the wire bonding step, a molding step for hermetically molding, using the plastic resin, the predetermined volume including the semiconductor chip 1, the inner leads 8 of the lead frame and the metal wires 7 is carried out, thus to form the plastic resin body 9. The molding step is followed by a trimming and forming step in which lead supporting dambars (not shown) are cut and a plurality of outer leads (not shown) of the lead frame are trimmed and formed into a predetermined bent shape.
In the plastic BGA package produced through the above process, the semiconductor chip is electrically connected to the inner leads of the lead frame by means of the plurality of the metal wires, which metal wires are bonded to the chip and to the inner leads in the wire bonding step. In addition, the outer leads of the lead frame are exposed to the outside of the plastic resin body hermetically packaging the predetermined volume including the semiconductor chip, the inner leads of the lead frame and the metal wires. However, the above plastic BGA package has a problem that it is very difficult to achieve the recent trend of diminution and thinness of the package. Furthermore, when a plurality of above packages will be used together in order to enlarge memory capacity, the packages are inevitably arrayed horizontally due to the outer leads exposed to the outside, thus to waste space.